The instant invention relates to high temperature resistant seals, such as those capable of withstanding continuous exposure to temperatures in excess of 2,000.degree. F., and more particularly to a high temperature resistant seal for a catalytic converter and to a method of making the seal.
Catalytic converters have generally been found to be effective for catalytically treating the exhaust gases of internal combustion engines. In this regard, a conventional catalytic converter generally comprises a relatively fragile monolithic catalyst structure including a ceramic monolith element having a catalyst, such as platinum, deposited thereon, a metal housing having inlet and outlet ends and a supporting seal for supporting the catalyst structure in the housing so that substantially all of the exhaust gases entering the inlet end of the housing pass through the monolithic catalyst structure and outwardly through the outlet end of the housing. However, the heretofore available supporting seals for catalytic converters have generally been found to be less than satisfactory for both cushioning the catalyst structures thereof against breakage resulting from physical shocks and for sealing between the catalyst structures thereof and their respective housings. It has been found that this is partially due to the fact that because the internal components of catalytic converters can be exposed to temperatures of up to 2,000.degree. F., the number and types of materials which are available for use as supporting seals in catalytic converters is somewhat limited. One of the most common materials utilized for such seals is stainless steel wire which has been formed, woven, and/or compacted into various configurations. However, seals made from stainless steel wire inherently have void spaces which permit certain quantities of exhaust gases to pass therethrough. Accordingly, there is a recognized need for a more effective supporting seal for supporting the monolithic catalyst structure of a catalytic converter in the housing thereof.
The instant invention provides a new high temperature resistant seal which can be effectively utilized for sealing between the catalyst structure of a catalytic converter and the housing thereof. Specifically, the seal of the instant invention is made from a high temperature resistant material which comprises between approximately 28 and 80 dry weight percent of ceramic fibers capable of withstanding continuous exposure to temperatures in excess of 2,000.degree. F. and between approximately 20 and 50 dry weight percent of high aspect ratio vermiculite (aspect ratio equals length or width/thickness). The vermiculite has an aspect ratio of at least approximately 10 and a mean particle size of less than approximately 50 microns, and it is operative for binding the ceramic fibers together to maintain the seal material in a substantially solid compressible form. The high temperature resistant seal material preferably further includes between approximately 5 and 60 dry weight percent of low temperature expanding vermiculite (LTEV) and the high aspect ratio vermiculite is preferably operative for binding both the ceramic fibers and the LTEV together to maintain the seal material in a substantially solid compressible form. The ceramic fibers preferably comprise alumina-silica fibers which have a melting point of approximately 3,260.degree. F. and which are capable of withstanding continuous exposure to temperatures of up to 2,300.degree. F. Further, the fibers preferably comprise relatively long fibers of relatively small diameter so that they are able to resiliently flex to absorb shocks applied to the seal.
The high temperature resistant seal of the subject invention is preferably made by forming a mixture comprising between approximately 28 and 80 dry weight percent of ceramic fibers capable of withstanding continuous exposure to temperatures in excess of 2,000.degree. F., between approximately 20 and 50 dry weight percent of an aqueous dispersion of high aspect ratio vermiculite and preferably also between approximately 5 and 60 dry weight percent of LTEV. The high temperature resistant seal is formed by applying this mixture to the exterior surface of a monolithic catalyst structure and heating the catalyst structure and the seal mixture to a temperature sufficient to evaporate substantially all of the water from the seal mixture. In this connection, when the ceramic fibers and the LTEV are mixed with an aqueous dispersion of high aspect ratio vermiculite, the vermiculite acts to bind the ceramic fibers and the LTEV together so that when the water is evaporated from the seal mixture the resultant material has a substantially solid compressible form.
It has been found that a high temperature resistant material of the above described type can be utilized for forming a supporting seal element which is capable of effectively sealing between the monolithic catalyst structure of a catalytic converter and the housing thereof and/or for supporting the monolithic catalyst structure in the housing. The high temperature resistant material is preferably formed around the monolithic catalyst structure so that it encircles the latter to effect a seal between the catalyst structure and the housing thereof. Further, it has been found that a seal formed by this procedure is generally sufficiently resiliently compressible to enable it to cushion the monolithic catalyst structure of a catalytic converter against breakage due to externally applied physical shocks.
Accordingly, it is primary object of the instant invention to provide an effective seal for a catalytic converter which is capable of withstanding continuous exposure to temperatures in excess of approximately 2,000.degree. F.
Another object of the instant invention is to provide an effective method of forming a high temperature resistant seal which is capable of withstanding continuous exposure to temperatures in excess of 2,000.degree. F.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawing